I took a photo right away, but was then worried that my new caecilian friend would slip forward into the stream and escape my camera. So I thought I could perhaps deter it by gently blocking its forward progress with my hand, and then pick it up with my other hand to move it to a less escapable area for more photos. As soon as it became aware of my blocking hand, it freaked out and began thrashing and flipping. I tried to grab it, but it was slippery and strong and I couldn't get a grip before it had managed to land in the water, where it quickly disappeared.
Caecilian expert Dr. David Gower confirmed my ID of Ichthyophis, and also clarified that a species-level ID would be impossible without significantly more detailed photos of the head, ventral side, etc. I was very lucky to see a caecilian at all, and even luckier to get an in situ photo, so I'm not bothered by the lack of a species-level ID.